Kanye blasts Kim's ex in live TV performance

Kanye West performs Bound 2 on Late Night with Jimmy Fallon. Photo / AP

Rapper Kanye West has taken aim at his girlfriend Kim Kardashian's ex Ray J by branding him lame and questioning his manhood during a surprise US TV performance.

West appeared on Late Night with Jimmy Fallon to play his new single Bound 2 with music veteran Charlie Wilson.

He used his stage time to take a subtle jab at Ray J at the top of the song.

However, West stopped short of mentioning the One Wish singer by name - instead, he namechecked Ray J's only sibling, R&B star Brandy, to make it clear to fans who he was referring to.

"Brandy's little sister lame, man, he know it now/When a real brother hold you down you supposed to drown," West said.

West and Wilson were backed onstage by presenter Jimmy Fallon's house band, hip-hop group The Roots.

Ray J famously featured in a 2003 sex tape with Kardashian, which leaked online in 2007. He recently courted controversy by releasing the song I Hit It First, reportedly about the socialite, who gave birth to West's daughter, North, in June.

On the track, he sings: "She might move on to rappers and ballplayers/ But we all know I hit it first ... I had her head going north and her ass going south. But now baby chose to go West... no matter where she goes or who she knows she still belongs in my bed."

The single's cover art even featured a pixellated photo of what appeared to be the reality TV star in a bikini, while a Kardashian lookalike was chosen to star in the accompanying video.

Watch West's performance of Bound 2 here.

- AAP